The formation and maturation of calcium phosphates prepared from physiological-like solutions is being studied with a variety of ultrastructural and physical-chemical techniques such as electron microscopy, x-ray diffraction, B-E-T surface area methods, and standard analytical chemistry procedures. Topics of current interest include (1) the effect of ionic fluoride, magnesium, and carbonate on physical properties of crystalline apatite such as crystallinity, specific surface area, and particle morphology, and (2) the effect of these ions on the formation, growth, and stability of precursors to the apatite phase.